The present invention relates to a capacitor discharge type internal combustion engine ignition device.
A capacitor discharge type internal combustion engine ignition device is comprised of an ignition coil; an ignition capacitor provided at the primary side of the ignition coil and charged by an output voltage of a predetermined power supply at one polarity; a discharge thyristor, which becomes an on-state when an ignition signal is given and discharges a charge of the ignition capacitor through the primary coil of the ignition coil; a signal generating portion for generating a signal to obtain rotational information on the internal combustion engine; and an ignition control portion which gives the ignition signal to the discharge thyristor at an ignition position (a rotational angle position of a crank shaft at a time of performing an ignition operation) of the internal combustion engine decided based on the rotational information obtained from the signal generated by the signal generating portion.
As for the power supply to charge the ignition capacitor, an exciter coil is often used, which is provided inside a magneto-generator driven by the internal combustion engine and synchronizes with rotation of the engine so that an alternating voltage is induced.
In recent years, in order to purify an exhaust gas of the engine and attempt to reduce a fuel cost, it is necessary for the engine to have complex ignition characteristics. For this reason, there are frequent cases where a microcomputer is installed in the ignition control portion and the ignition position is decided in a software manner.
In the case where the ignition signal is generated at the ignition position decided in the software manner by using the microcomputer, a reference position is set at a position sufficiently advanced more than the rotational angle position corresponding to a top dead center of the internal combustion engine, and a time required for the engine to rotate to the ignition position arithmetically operated from the reference position is found as an ignition position detection time (time to be measured by the ignition timer for detecting the ignition position). When the reference position is detected, an ignition timer is allowed to start measuring the ignition position detection time and generate the ignition signal when the measurement has been completed.
As described above, in the internal combustion engine which controls the ignition position by using the microcomputer, since it is necessary to detect the reference position as the basis for measuring the ignition position decided in the software manner and the ignition position at a starting time and an extremely low speed state, the signal generating portion is comprised in such a manner that a reference position detection signal is generated at the reference position set at a position sufficiently advanced more than the rotational angle position of the crank shaft corresponding to the top dead center of the engine, and the ignition position detection signal for extremely low speed state is generated at the position adequate as the ignition position at the starting time and the extremely low speed state of the internal combustion engine.
Further, the ignition control portion is provided with an ignition control portion for extremely low speed state for giving the ignition signal to the discharge thyristor when the ignition position detection signal for extremely low speed state is generated and an ignition control portion for steady state for giving the ignition signal to the discharge thyristor at the ignition position decided based on the rotational information on the internal combustion engine, which is obtained from the output signal of the signal generating portion.
In the case where the ignition position is decided by using the microcomputer, if a battery is provided, the microcomputer can be operated from the starting time of the engine and, therefore, there arises no problem at all. However, in the case where no battery is provided or in the case where there is a necessity to make it possible to operate the engine even when the battery is exhausted for safety reason, it is necessary to give a power supply voltage to the microcomputer by an output of a generator mounted on the engine. For example, in an outboard motor, the engine is required to operate even when the battery is exhausted. For this reason, in the ignition device of this type, a control power supply circuit is provided, which rectifies a negative half-wave output of the exciter coil not used for charging the ignition capacitor and generates a constant direct current voltage so that, from this power supply circuit, the power supply voltage is given to the ignition control portion.
In a battery-less ignition device having a microcomputer provided with power voltage from the output of the control power supply circuit fed by the generator mounted on the internal combustion engine instead of a battery, since the microcomputer is not allowed to normally operate until the output voltage of the generator is raised to a certain level at a starting time of the engine, the ignition operation can not be performed as long as the rotational speed of the internal combustion engine is low. Further, even when the microcomputer can be normally operated, as long as the rotational speed of the engine is low, since fluctuation in the rotational speed accompanied by a stroke change of the engine is large, it is difficult to accurately measure the ignition position arithmetically operated by the microcomputer, thereby it is not possible to stably perform the ignition operation.
For this reason, in the battery-less ignition device, a signal is generated from the generator or a signal generator mounted on the engine at a position adequate as the ignition position at the starting time and the extremely low speed state of the engine, and when this signal has been generated, the ignition signal is given to the discharge thyristor through a hardware circuit, so that an ignition at the starting time and the extremely low speed state (a speed region below an idling rotational speed) is stably performed.
As described above, in the battery-less capacitor discharge type ignition device which decides the ignition position in the software manner by using the microcomputer, in order to stably perform the ignition at the starting time and the extremely low speed state of the engine, the ignition control portion for extremely low speed state is provided, wherein the ignition signal is given to the discharge thyristor through the hardware circuit. However, in a conventional ignition device of this type, since the power supply voltage was given to the ignition control portion for steady state provided with the microcomputer and to the ignition control portion for extremely low speed state from the same power supply circuit, there was a problem that the ignition control portion for extremely low speed state delays in starting an operation at the starting time of the engine.
That is, since the microcomputer constantly consumes electric power, when the rotational speed of the engine is low and a peak value of the negative half wave output voltage of the exciter coil is not in a sufficiently high level state (in a state whereby the peak value of the output voltage of the negative half-wave of the exciter coil barely reaches the power supply voltage of the microcomputer), even if the power supply circuit outputs the voltage of a value (5V) necessary for operating the microcomputer while the exciter coil generates the negative half-wave output voltage, the output of the control power supply circuit stops as soon as the exciter coils enters a time period for outputting a positive half-wave voltage. Accordingly, until the control power supply circuit, which drives the microcomputer, is put into a state of stably outputting a voltage held at a set value, it is necessary to wait until the rotational speed of the engine is further increased so that the output voltage of the exciter coil is increased. For this reason, in the case where the power supply voltage is given to the ignition control portion for extremely low speed state by the same power supply circuit as the power supply circuit driving the microcomputer, there arose problems that a start of the operation of the ignition control portion for extremely low speed state is delayed, a starting characteristic of the engine is deteriorated and an ignition operation at an idling time is unstable.
Hence, an object of the present invention is to provide a capacitor discharge type internal combustion engine ignition device, wherein a rotational speed of which the ignition control portion for extremely low speed state starts an operation is sufficiently lowered so that a starting characteristic of the internal combustion engine can be improved and an idling rotation can be stably performed.
The present invention is applied to a capacitor discharge type internal combustion engine ignition device which comprises: an exciter coil provided inside a magneto-generator to be driven by an internal combustion engine; an ignition coil; an ignition capacitor provided at an primary side of the ignition coil and charged by a positive half-wave output voltage of the exciter coil at one polarity; a discharge thyristor which becomes an on-state when an ignition signal is given and discharges a charge of the ignition capacitor through the primary coil of the ignition coil; a control power supply circuit which converts the output voltage of the exciter coil into a direct current voltage; a signal generating portion for generating a reference position detection signal at a reference position set at a position sufficiently advanced more than a rotational angle position of a crank shaft which corresponds to a top dead center of the internal combustion engine and generating an ignition position detection signal for extremely low speed state at a position adequate as an ignition position at the starting time and the extremely low speed state of the internal combustion engine; an ignition control portion for extremely low speed state for giving an ignition signal to the discharge thyristor when the ignition position detection signal for extremely low speed state is generated; and an ignition control portion for steady state for giving the ignition signal to the, discharge thyristor at the ignition position decided based on rotational information on the internal combustion engine obtained from an output signal of the signal generating portion, and the ignition control portion for extremely low speed state and the ignition control portion for steady state operate with a direct current power supply voltage which is obtained by the control power supply circuit.
The present invention provides a first power supply circuit for generating a constant direct current voltage for operating the ignition control portion for steady state when the output voltage of the exciter coil is equal to or more than a set value and a second power supply circuit for generating the direct current voltage for operating the ignition control portion for extremely low speed state since when the output voltage of the exciter coil is in a state of being below the set value.
Further, the ignition control portion for extremely low speed state is comprised in such a manner as to start the operation at the power supply voltage lower than the power supply voltage (usually 5V) of the ignition control portion for steady state.
Since the ignition control portion for extremely low speed state consumes electric power only for a few period when the ignition signal for extremely low speed state is generated, even when a rotational speed of the engine is low and the exciter coil is in a state where an output necessary for stably operating the ignition control portion for steady state is unable to be generated from the first power supply circuit, the power supply voltage necessary for operating the ignition control portion for extremely low speed state can be stably generated from the second power supply circuit. For this reason, as described above, when the second power supply circuit for exclusive use of the ignition control portion for extremely low speed state is provided, the operation of the ignition control portion for extremely low speed state can be started at a rotational speed lower than the rotation speed whereby the ignition control portion for steady state starts the operation so that the starting characteristic of the engine can be improved and an idling rotation can be stably performed.
As for the magneto-generator used for operating the capacitor discharge type internal combustion engine ignition device, a magneto-generator is frequently used, which comprises: a magnetic rotor having a rotational body mounted on a crank shaft of the internal combustion engine and one permanent-magnet mounted on an outer periphery of the rotor and comprising a three pole magnetic field by the permanent-magnet and an outer periphery portion of the rotational body abutting against the permanent-magnet; and a stator having an iron core with a magnetic pole portion opposing to the magnetic filed of the magnetic rotor and an exciter coil wound around the iron core, which outputs from the exciter coil an alternating current voltage of one and a half cycle where a first negative half-wave voltage and positive half-wave voltage and a second negative half-wave voltage appear in order.
In the case where such a magneto-generator is used, the signal generating portion can be comprised of the exciter coil and a waveform shaping circuit which waveform-shapes the first and the second negative half-wave voltages outputted by the exciter coil, respectively and converts them into the first and the second pulse signals of a rectangular waveform shape.
In this case, the magneto-generator is provided so that a rising edge position or a falling edge position of the second pulse signal corresponds to a position adequate as an ignition position at the starting time and the extremely low speed state of the internal combustion engine.
Further, taking each rising edge or falling edge of the first and the second pulse signals as the ignition position detection signal for the extremely low state, the ignition control portion for extremely low speed state is comprised so as to provide an ignition signal to the discharge thyristor at the position where the rising edge or the falling edge of the first pulse signal is appeared and where the rising edge or the falling edge of the second pulse signal is appeared. This ignition control portion for extremely low speed state is comprised of a hardware circuit.
The ignition control portion for steady state is comprised so that a microcomputer operates with the direct current voltage obtained from the first power supply circuit, and taking the rising edge or the falling edge of the first pulse signal as the reference position detection signal, the microcomputer performs an arithmetical operation of the ignition position in each rotational speed of the internal combustion engine and a detection of the operated ignition position, and the microcomputer gives the ignition signal to the discharge thyristor when the operated ignition position is detected.
When comprised as described above, even before the exciter coil generates the positive half-wave output voltage (before the ignition capacitor is charged), the ignition signal is given to the discharge thyristor. However, even though the ignition signal is given with the ignition capacitor being in a non-charged state, the discharge thyristor is not the on-state, so an ignition operation is not performed, thereby no trouble occurs for the ignition of the engine.
When comprised as described above, since there is no need to provide a signal generator separately from the magneto-generator, the ignition position can be decided by the arithmetical operation without the constitution of the engine made complex, so that the internal combustion engine ignition device capable of dealing with various ignition characteristics can be obtained.
In the present specification, the ignition signal given to the discharge thyristor from the ignition control portion for extremely low speed state comprising the hardware circuit is referred to as xe2x80x9ca hardware ignition signalxe2x80x9d in a sense that it is the ignition signal given from the hardware circuit. Further, the ignition operation performed by the hard ignition signal is referred to as a hard ignition.
On the other hand, the ignition signal given to the discharge thyristor at the ignition position arithmetically operated by allowing the microcomputer to execute a predetermined software is referred to as xe2x80x9ca soft ignition signalxe2x80x9d in a sense that it is the ignition signal to be generated at the ignition position decided in the software manner. Further, the ignition operation performed by the soft ignition signal is referred to as a soft ignition.
In a preferred mode of the present invention, an ignition signal cancel switch is further provided, which becomes an on-state when the cancellation command is given and bypasses the ignition signal given to the discharge thyristor from the ignition control portion for extremely low speed state. In this case, the microcomputer of the ignition control portion for steady state is programmed in such a manner as to comprise: reference position detection means for discriminating the first pulse signal and the second pulse signal from signal widths of the first and the second pulse signals and intervals of generating the first and the second pulse signals and detecting the rising or the falling edge of one of the discriminated signals as the reference position; rotational speed detection means for finding the data to detect the rotational speed of the internal combustion engine by using at least one of the first and the second pulse signals; ignition position arithmetical operation means for arithmetically operating the ignition position of said internal combustion engine for the detected rotational speed in the form of a time required for the crank shaft of the engine to rotate from said reference position to the ignition position; ignition position detection means for starting measurement of the ignition position when the reference position is detected and giving the ignition signal to the discharge thyristor when the measurement of the ignition position has been completed; and cancellation command generating means for generating a cancellation command when the rotational speed of the internal combustion engine exceeds a set value.
In the case where the cancel switch is provided as described above and the rotational speed of the internal combustion engine exceeds the set value and the microcomputer is in an operating state, when the cancel switch is the on-state so that the ignition signal given to the discharge thyristor from the ignition control portion for extremely low speed state is bypassed from the discharge thyristor, the discharge thyristor becomes the on-state by the ignition signal given to the discharge thyristor by the falling or the rising of the first pulse signal at the steady time operating time, thereby making it possible to put the ignition capacitor into a state of not being charged and prevent the engine from causing an accidental fire.
The ignition control portion for extremely low speed state may comprises: an ignition signal supply capacitor charged by the output voltage of the second power supply circuit through a current limiting element and between a gate and a cathode of the discharge thyristor; a transistor provided in such a manner as to become an on-state the first and the second pulse signals as base signals and bypass the charge current of the ignition signal supply capacitor from the capacitor; and a diode for linking between the ignition signal supply capacitor and the transistor so that the charge of the ignition signal supply capacitor is discharged through the transistor when the transistor is the on-state, wherein the ignition signal is given to the discharge thyristor by the falling edges of the first pulse signal and the second pulse signal.
In the above described example, though the negative half-wave output voltage is shaped into a pulse waveform so as to obtain the reference position detection signal and the ignition position detection signal for extremely low speed state, the reference position detection signal and the ignition position detection signal for extremely low speed state may be obtained from the output of the signal generator mounted on the internal combustion engine. In this case, the signal generating portion is mounted on the internal combustion engine, and can be comprised of a signal generator for generating a first signal when the rotational angle position of the crank shaft of the engine corresponds to the reference position and generating a second signal when the rotational angle position of the internal combustion engine corresponds to the position adequate as the ignition position at the starting time and the extremely low speed state and a waveform shaping circuit for shaping the first and the second signals outputted by the signal generator into predetermined waveforms, respectively and outputting them as the reference position detection signal and the extremely low speed state ignition detection signal.